1. Field of the Invention
The present invention relates to a broadcast receiving apparatus employed for reception of, for example, terrestrial digital broadcasting.
2. Description of the Related Art
A cellular telephone for a mobile communications system called Third Generation has a function of receiving terrestrial digital broadcasting (“one-segment broadcasting”) (cf., for example, W. Kameyama and T. Hanamura, “Revised Edition of Digital Broadcasting Textbook I”, Impress, October 2004, pp. 85-87). In the terrestrial digital broadcasting, image data is encoded in H.264/AVC and speech data is encoded in MPEG-2 AAC. The encoded image data and speech data are called “Elementary Streams” (hereinafter called ES), which are superposed on a transport stream in MPEG-2 SYSTEM as Packetized Elementary Stream packets (PES packets) and then transmitted.
Transport stream packets (TS packets) are aligned in the transport stream. In the TS packets, attribute information which indicates the type (attribute) of the bit streams including the video information and audio information, reference clock information which is called a program time standard reference value (PCR) for synchronization in the bit streams and media, and the like can be stored. The TS packets are transmitted from the transmitting side to the receiving side in a wireless or wired method.
The received TS packets are temporarily stored on the receiving side. When the TS packets including the PCR are received, the PCR is used for the control of the STC counter which counts a system time clock (STC) to establish clock synchronization with the transmitting side. More specifically, the receiving side extracts a value by sampling the PCR of the transmitting side at 27 MHz and adjusts the STC by comparing the sampled value with the STC value of the receiving side, i.e. the receiving side executes what is called clock recovery.
In addition, when the STC value counted by the STC counter is greater than a display time stamp (PTS) included in the PES packets, the receiving side reproduces the ES in the PES packets, in synchronization with the STC value. As the stream reproduction method, a time shift reproduction mode is employed, besides a general reproduction mode of sequentially decoding and reproducing the image data and speech data in the TS packets received from the broadcast wave.
In the time shift reproduction mode, the received TS packets are stored in a buffer (time shift storage) while the user cannot view. When the user becomes in a state of viewing, the images and speech in the stored TS packets are sequentially decoded and reproduced while the received TS packets are sequentially stored in the buffer.
In the time shift reproduction mode, the reproduction may be executed at an equal double speed, but a higher speed since the TS packets stored in the buffer are reproduced. When the high-speed reproduction is executed during the time shift reproduction and the speed of reproduction of the stored data remains higher than the speed of storing the input from the broadcast wave, the TS packets stored in the buffer are reduced. After that, when the buffer becomes free, the time shift reproduction mode is changed to the general reproduction mode of reproducing the image data and the speech data without storing the TS packets demultiplexed from the broadcast wave in the buffer.
Therefore, in the time shift reproduction mode, the process of storing the TS packets demultiplexed from the broadcast wave in the buffer and the process of reproducing the TS packets stored in the buffer need to be executed simultaneously.
In addition, for example, a NAND-type flush memory is often used for the buffer. In this case, a data process sequence can be controlled easily by transferring the data to the buffer with the TS packets of a relatively small unit, and the time shift reproduction mode can be returned easily and smoothly to the general reproduction mode by high-speed reproduction or the like. However, overhead of the data transmission is great since the processes are executed in a relatively small unit.
On the other hand, when the data is transferred to the buffer with the TS packets of a relatively great unit, the overhead can be reduced. However, if the time shift reproduction mode is not changed to the general reproduction mode at an appropriate timing, images and sound are interrupted and the reproduction quality is deteriorated.
Conventionally, magnitude of the overhead of the transferred data causes a problem due to the size of the TS packets used in the time shift reproduction mode and transferred to the buffer or the reproduction quality is deteriorated during process of changing the time shift reproduction mode to the general reproduction mode.